Query : 2016A&A...595A..33T

2016A&A...595A..33T - Astronomy and Astrophysics, volume 595A, 33-33 (2016/11-1)

Cosmic-ray energy spectrum and composition up to the ankle: the case for a second Galactic component.


Abstract (from CDS):

Motivated by the recent high-precision measurements of cosmic rays by several new-generation experiments, we have carried out a detailed study to understand the observed energy spectrum and composition of cosmic rays with energies up to about 1018 eV. Our study shows that a single Galactic component with subsequent energy cut-offs in the individual spectra of different elements, optimised to explain the observed elemental spectra below ∼1014eV and the "knee" in the all-particle spectrum, cannot explain the observed all-particle spectrum above ∼2x1016eV. We discuss two approaches for a second component of Galactic cosmic rays - re-acceleration at a Galactic wind termination shock, and supernova explosions of Wolf-Rayet stars, and show that the latter scenario can explain almost all observed features in the all-particle spectrum and the composition up to ∼1018eV, when combined with a canonical extra-galactic spectrum expected from strong radio galaxies or a source population with similar cosmological evolution. In this two-component Galactic model, the knee at ∼3x1015eV and the "second knee" at ∼1017eV in the all-particle spectrum are due to the cut-offs in the first and second components, respectively. We also discuss several variations of the extra-galactic component, from a minimal contribution to scenarios with a significant component below the "ankle" (at ∼4x1018eV), and find that extra-galactic contributions in excess of regular source evolution are neither indicated nor in conflict with the existing data. We also provide arguments that an extra-galactic contribution is unlikely to dominate at or below the second knee. Our main result is that the second Galactic component predicts a composition of Galactic cosmic rays at and above the second knee that largely consists of helium or a mixture of helium and CNO nuclei, with a weak or essentially vanishing iron fraction, in contrast to most common assumptions. This prediction is in agreement with new measurements from LOFAR and the Pierre Auger Observatory which indicate a strong light component and a rather low iron fraction between ∼1017 and 1018eV.

Abstract Copyright: © ESO, 2016

Journal keyword(s): diffusion - stars: winds, outflows - ISM: supernova remnants - galaxies: ISM - cosmic rays

Simbad objects: 2

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Number of rows : 2
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 SNR G347.3-00.5 SNR 17 12 27 -39 41.2     12.27     ~ 694 1
2 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 13454 0

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